1. Field of the Invention
The present invention relates to a silica layer comprising an organic silicon compound and a carbon-containing silica layer containing carbon, and also to an antireflection film having an antireflection multilayered article formed of these silica layers.
2. Related Art
Transparent boards made of glass, plastic, etc. are used in various displays including liquid-crystal displays, plasma displays, and CRTs for computers, word processors, television sets, and indicating panels, etc. Such transparent boards are also used in indicators for instrumentation, etc., and rear-view mirrors, goggles, window panes,etc. When trying to read characters, symbols and other information through these transparent boards, one may have difficulty doing so due to reflection of light on their transparent surface.
To overcome this difficulty, one technique available today is to arrange an antireflection multilayered article having layers of different refractive indices superposed on a substrate film to form an antireflection film, and then to adhere the antireflection film to the surface of a transparent board, for prevention of light reflection.
It is known to be preferable to provide a small refractive index layer as the outermost layer (substantially opposite to the substrate of the antireflection film) of the antireflection multilayered article for efficient prevention of light reflection, and a silica layer is suitably used as this small refractive index layer. It is also known to be preferable to provide a plurality of layers inward of the outermost layer (i.e., between the substrate and the outermost layer of the antireflection film), which have refractive indices greater than that of the outermost layer.
However, due to the fact that the density of a silica layer is generally proportional to its refractive index, to decrease the refractive index of a silica layer used as the outermost layer, low density silica layer must be used. However, in the low density silica layer, there are many voids, and when this silica layer is used for a long period of time and/or under high temperature and high humidity, these voids are subjected to inversion of water molecules to change the reflective index of the silica layer.
Further, in many antireflection multilayered articles of conventional antireflection films, their outermost layer is formed of a silica layer, but the layers other than the outermost layer (i.e., the layers having refractive indices different from that of the outermost layer) are made from materials other than silica. For example, in many antireflection multilayered articles having a low refractive index layer, a medium refractive index layer, and a high refractive index layer superposed on a substrate film, a silica layer is used as the low refractive index layer which is the outermost layer, and titanium oxide layers are used as the medium and high refractive index layers. Further, these medium and high refractive index layers are usually formed by sputtering, etc.